This invention relates to a multi-pole circuit interrupter and, more particularly, to a multi-pole circuit interrupter having a central pole unit and side pole units disposed on the both sides of the central pole unit.
FIGS. 1 to 3 illustrate one example of a conventional multi-pole circuit interrupter. FIG. 1 is a front view of the conventional multi-pole circuit interrupter with the cover partly cut away, FIG. 2 is a sectional side view taken along line II--II of FIG. 1, and FIG. 3 is a sectional view taken along line III--III of FIG. 2.
In these figures, the multi-pole circuit interrupter comprises an electrically insulating housing 1 composed of a cover 1A and a base 1B. The housing 1 includes two outer walls 1a and two partition walls 1b defining three compartments therebetween in which a central pole unit A and side pole units B are disposed. On the housing base 1B, a stationary contact 2, which has a stationary contact element 2a on its one end and which has a terminal 17B including a terminal screw hole 2b at the other end, is fixedly mounted. An arc runner 3 and an electrically insulating casing 4 are mounted to the stationary contact 2, and a frame 5 is also mounted to the base 1B by screws 6 (only one is shown). The frame 5 supports at its projection 5a an operating handle 7 so that the operating handle 7 is rotatable about the projection 5a. The operating handle 7 has mounted thereon a cradle 8 pivotable relative to the operating handle 7.
A toggle link 10, which includes an upper toggle link 10a and a lower toggle link 10b pivotally connected to the upper toggle link 10a by a knee pin 11, is connected to the operating handle 7 by an upper toggle link pin 9 at the upper end of the upper toggle link 10a. The lower end of the lower toggle link 10b is connected by a pin 14 to a cross bar 13 which is rotatably mounted with respect to the base 1B. The knee pin 11 of the toggle link 10 is biased toward the operating handle 7 by a tension spring 12 connected between the pin 11 and the handle 7, thus maintaining the upper toggle link 10a in engagement with the pin 9. A movable contact arm 15 having a movable contact element 15a secured thereon is rotatably mounted on the cross bar 13 by a shaft 16. The movable contact arm 15 is electrically connected through a flexible conductor 18 to a terminal conductor 17 which is secured to the base 1B and has a terminal 17A with a screw hole 17a.
The circuit interrupter also comprises an electromagnetic trip device including an electromagnetic device 19 which has a movable plunger 19a. A thermally responsive trip device having a bimetal 20 with an adjusting screw 20a is also provided. In order to pick up the movements of two kinds of trip devices, a trip bar 21 which is rotated by the screw 20a or the plunger 19a is provided. The trip bar 21 is in engagement with a latch 22 which is in engagement with a latch 23 to releasably latch the cradle 8. An arc extinguisher 24 including a plurality of arc extinguishing plates 24a is also disposed within the housing.
As is well known in the art, the operating handle 7 as above described is provided only in the central pole unit disposed within the central compartment. However, since all the movable contact arms 15 of the pole units A and B are connected to each other by the cross bar 13, they move in unison when the central pole unit A is manually moved or when at least one of the three pole units A and B is tripped.
When the circuit interrupter is in the ON position shown in FIGS. 1 to 3, the current flows from the stationary contact 2 to the terminal conductor 17 through a stationary contact element 2a, the movable contact element 15a, the movable contact arm 15 and the flexible conductor 18. When the operating handle 7 is moved in the direction of an arrow 25, the upper end of the tension spring 12 is moved beyond the dead center of the line of action of the spring 12, causing the tension spring 12 to collapse the toggle link 10 to move the movable contact arm 15 upwards together with the cross bar 13 until the movable contact assembly takes the OFF position.
When a very large current flows through the circuit interrupter in the ON position shown in FIG. 1, the electromagnetic trip device is actuated to push out the plunger 19a from the electromagnetic device 19. Alternatively, when an overcurrent flows through the circuit interrupter in the ON position shown in FIG. 1, the thermally responsive trip device is actuated to push the trip bar 21 by the adjusting screw 20a. In either case, the trip bar 21 is rotated to rotate the latch member 22 and then the latch 23 rotates to release the cradle 8 under the action of the spring 12 which biases the cradle 8 to rotate clockwise. The cradle 8 is then rotated clockwise in FIG. 3 so that the toggle link pin 9 moves overcenter causing the toggle link 10 to collapse to rotate the movable contact arm 15 together with the cross bar 13 about the shaft 16 until they are brought into the TRIP position in which the movable contact element 15a is separated from the stationary contact element 2a.
With the multi-pole circuit interrupter as above described, the stationary contacts 2 in the three pole units A and B have the same configuration as shown in FIGS. 1 and 3. Therefore, the distance y between a center line x passing through the centers of the stationary contact element 2a, the movable contact arm 15 and the arc extinguisher 24 of the respective pole units A and B equals the distance z between center lines of the terminals 17A and 17B or center lines passing through the terminal screw holes 2b and 17a. Therefore, as best seen in FIG. 1, the side walls 1a are significantly thinner at the portion adjacent to the main mechanism including the stationary contact elements 2a, the movable contact arm 15 and the arc extinguisher 24 than the portion adjacent to the terminals 17A and 17B and than the partition walls 1b disposed between the pole units A and B. If it is desired to increase the strength of the side walls 1a of the housing 1, the thickness of the side walls must be increased so that the overall width dimension of the housing 1 must also be increased.